(1) Field of the Invention
The present invention relates to a photosensitive material having a high sensitivity. More particularly, it relates to a photosensitive material which has a high photosensitivity to rays having a wave length included in the semiconductor laser oscillation wave length region and is valuable as a photosensitive material for a laser printer, especially a semiconductor laser printer.
(2) Description of the Prior Art
Many photosensitive materials such as Se, Se-Te, CdS, ZnO and organic photoconductors are known as the photosensitive material having a sensitivity to rays having a wave length included in the visible ray wave length region, that is, the wave length region of from 370 to 720 nm. Some of these photosensitive materials have already been used practically for electrophotographic copying machines or laser printers comprising an He-Ne laser as the beam source. However, there have hardly been known photosensitive materials having a sensitivity to rays having a wave length included in the semiconductor laser oscillation wave length region, that is, the near infrared ray wave length region, but only CdS, As-Te-Se and phthalocyanine photosensitive materials are known as such photosensitive material. However, CdS and As-Te-Se photosensitive materials are harmful and poisonous, and use of these photosensitive materials is not preferred because of occurrence of environmental pollution and also because of necessity of special consideration to maintenance of the safety in the manufacturing process. Furthermore, the As-Te-Se photosensitive material is defective in that a vacuum evaporation deposition apparatus should be used for the production thereof and the manufacturing process is complicated. Although Cds has a good photosensitivity, it is defective in that since the charging degree is low, a special charging process should be adopted.
Since a phthalocyanine pigment is cheap and very low in the toxicity, researches have heretofore been made on application of the phthalocyanine pigment to copying machines, laser printers and the like as the photosensitive material in the field of electrophotography. A phthalocyanine pigment alone cannot be used for the production of a photosensitive material because it has no film-forming property or vacuum evaporation deposition thereof is very difficult. Accordingly, a photoconductive film is ordinarily formed by dissolving or dispersing the phthalcyanine pigment together with a binder in an organic solvent to form a photoconductive coating solution or dispersion and coating the solution or dispersion at a thickness of several microns to scores of microns after drying on an electroconductive substrate by means of a doctor blade, a bar coater, a roll coater or the like.
The photosensitive film of the phthalocyanine pigment prepared according to the above-mentioned process shows a so-called induction phenomenon in which the decay just after irradiation is very small, that is, the irradiation energy is not utilized at a high efficiency. Accordingly, the sensitivity of this photosensitive film is insufficient as the photosensitive material for a copying machine for electrophotography or a laser printer, and the sensitivity to rays having a wave length included in the semiconductor laser oscillation wave length region is especially low. Therefore, this film is still insufficient as the photosensitive material.
As means for overcoming the foregoing difficulties involved in the phthalocyanine photosensitive material, Japanese Laid-Open Patent Application No. 133037/78 proposes a method in which 2,5-bis(4'-dialkylaminophenyl)-1,3,4-oxadiazole or other electron-donative compound is incorporated in a photosensitive layer comprising copper phthalocyanine in an amount of 0.01 to 5 mole % based on the copper phthalocyanine.
We made examinations on the above-mentioned phtosensitive material comprising copper phthalocyanine and 2,5-bis(4'-dialkylaminophenyl)-1,3,4-oxadiazole in combination, and to our great surprise, it has been found that when 2,5-bis(4'-diethylaminophenyl)-1,3,4-oxadiazole is incorporated in copper phthalocyanine in an amount much larger than the amount taught by Japanese Laid-open Patent Application Ser. No. 133037/78 and the proportion of the amount of a binder resin in the photosensitive material is reduced as compared with the amount taught by the Japanese patent application, unexpectedly excellent photosensitive characteristics can be obtained.